Guanine-La complex supported onto SBA-15: A novel efficient heterogeneous mesoporous nanocatalyst for one-pot, multi-component Tandem Knoevenagel condensation-Michael addition-cyclization Reactions

In this work, we present a simple, environmentally-friendly and economical route for the preparation of a novel lanthanum (III) organometallic complex immobilized onto a highly stable mesoporous silica SBA-15 (La-guanine@SBA-15) using an inexpensive and simple method and available materials. This mesoporous heterogenized complex was comprehensively characterized using FT-IR, XRD, EDS, ICP, MAP, SEM, TGA and BET techniques. The catalytic activity of this mesoporous material was studied in one-pot multi-component tandem Knoevenagel condensation-Michael addition-cyclization reactions in order to prepare a series of benzo [a] pyrano [2, 3-c] phenazine and 4,4 '-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols) derivatives under green conditions. This catalyst exhibited highly recoverable and recyclable features in consecutive reaction runs. Besides, the products were obtained in high yields and short reaction times. In this sense, simple preparation of the catalyst from the commercially available materials, simple operation, high catalytic activity, short reaction times, high yields and the use of green reaction conditions in the mentioned organic synthesis are the most significant advantages of this protocol. In addition, this nanocatalyst was easily recovered, using simple filtration, and reused several times without significant loss of its catalytic efficiency. Moreover, the leaching, heterogeneity and stability of La-guanine@SBA-15 were studied by hot filtration test and ICP technique. Finally, stability of the catalyst after recycling was confirmed by SEM and FT-IR techniques.